On the generation of optical third-harmonic through quasi-phase-matching in quadratic nonlinear crystals

We investigate the simultaneous processes of optical frequency doubling and sum frequency generation in quasi-phase-matched quadratically nonlinear crystals. Specifically, we focus on lattices with domain thicknesses corresponding to the coherence lengths of the two cascaded parametric processes and explore the realistic scenario of a single crystal containing sequential domain segments, each independently satisfying quasi-phase-matching for optical frequency doubling and summing, respectively. We demonstrate that high conversion efficiencies to the third harmonic can be obtained from an arbitrary fundamental wavelength.